Active deformation in southern Italy, Sicily and southern Sardinia from GPS velocities of the Peri-Tyrrhenian Geodetic Array (PTGA)

Abstract

Campaign measurement (1995-2000) of Global Positioning System
\n(GPS) site velocities in southern Italy, Central Mediterranean
\narea, document differential displacements within the orogens rimming
\nthe Tyrrhenian Sea. Within the Southern Apennines, GPS
\nvelocities define two laterally juxtaposed belts of deformation, with
\ntranspression in the east and transtension in the west. In the east,
\n~8 mm/yr convergence between northern Murge-Gargano block and
\nthe International GPS System (IGS) site MATE is partitioned across
\n~east-west striking right-lateral faults, consistent with seismicity
\nand with the offshore geological record. To the south, in northern
\nCalabria, site velocities relative to MATE indicate transpression at
\n~5 mm/yr, not recorded by seismicity but consistent with the on-land
\nand offshore geological record. In contrast, site velocities along the
\nTyrrhenian Sea coast to the west diverge from MATE at 2-3.5 mm/yr,
\nand are consistent with the crustal extension documented by seismicity
\nand fault slip studies. The transpressional belt is tracked southward
\nacross the Ionian Sea by oblique convergence of central Sicily
\nsites (2-6 mm/yr) relative to the IGS site NOTO in the Hyblean block.
\nNorth-western Sicily sites display clockwise rotation, a pattern
\nreflected in the geological and paleomagnetic record. Ssignificant
\nhorizontal motion accompanies rotation in north-western Sicily and
\nis probably accommodated by west-northwest – east-southeast and
\nnortheast-southwest-striking right- and left-oblique faults, respectively,
\nconsistent with a regional ~north-northwest – south-southeast
\ntrending shortening axis. The ~east-west striking belt of contractional
\nearthquakes observed offshore northern Sicily is consistent with up
\nto ~10 mm/yr geodetic convergence between Sicily and Sardinia.
\nSouthern Sardinia sites exhibits differential velocities relative to the
\nIGS site CAGL, suggesting internal deformation which is not
\nrecorded by seismicity and might signal incipient fragmentation of
\nthe Sardinia margin in response to relative convergence with Sicily.